Passive Optical Networks (PONs) may be used as part of the implementation of next-generation access networks. With the large bandwidth of optical fibers, PONs can accommodate broadband voice, data, and video traffic simultaneously. Moreover, PONs can be built with existing protocols, such as Ethernet and Asynchronous Transfer Mode (ATM), which facilitate interoperability between PONs and other network equipment.
Transmissions within a PON are typically performed between an Optical Line Terminal (OLT) and Optical Network Units (ONUs). The OLT generally resides in a Central Office (CO) and couples the optical access network to a backbone, which can be an external network belonging to, for example, an Internet Service Provider (ISP) or a local exchange carrier. The ONU can reside in the residence or workplace of a customer and couples to the customer's network through a Customer-Premises Equipment (CPE).
PON communications can include downstream traffic and upstream traffic. Downstream traffic refers to the direction from an OLT to one or more ONUs, and upstream traffic refers to the direction from an ONU to the OLT. In the downstream direction, data packets may be broadcast by the OLT to all ONUs and are selectively extracted by their destination ONUs. In the upstream direction, the ONUs share channel capacity and resources, because there is generally only one link coupling the passive optical coupler to the OLT.
As the popularity of PONs increases, the number of deployed ONUs will increase. As a result, the power consumption of each ONU can no longer be ignored, and adding power mitigating features to ONU designs becomes increasingly important.